Add a warning for unbound constraints in the validating loader

Closes #2165
Added a new FAQ entry about unbound version constraints
added new dependency to Perforce object, updating some tests.
almost all unit tests passing after IOInterface dependency refactor.  no longer passing IOInterface into any Perforce methods
got all unit tests passing
Fixing bug not cleaning up workspaces.
Update SvnDownloader.php

added --ignore-ancestry to the switch statement because it can be a problem with svn:properties
Fixing delete client workspace bug.
Throw RuntimeException when ambiguous reference was found.
improve exception message
fix plural in exception message
Fixing perforce dev-master stored reference bug.
added new dependency to Perforce object, updating some tests.
almost all unit tests passing after IOInterface dependency refactor.  no longer passing IOInterface into any Perforce methods
got all unit tests passing
Fixing bug not cleaning up workspaces.
Fixing delete client workspace bug.
Fixing perforce dev-master stored reference bug.
Merge branch 'master' of https://github.com/clarkstuth/composer
Merge pull request #3 from clarkstuth/master

Fixing perforce driver/downloader bugs